For example, a conventional gate driver circuit is structured as follows. A capacitor is charged in advance by a dedicated power supply. In an initial stage of a transition period during which the semiconductor device as a switching element is turned on, a drive voltage is generated by boosting a drive power supply voltage based on the charged voltage of the capacitor. The generated drive voltage is supplied to the semiconductor device. In such a structure, a variable voltage generating section controls the charged voltage of the capacitor according to an instruction signal, by which the drive voltage is appropriately controlled and is used for high-speed switching of the semiconductor device. Further, the electric charge stored in the capacitor has been discharged by the end of the Miller period that has change in the drain-source voltage of a MOSFET (metal-oxide-semiconductor field-effect transistor) as a switching element (see Patent literature 1).
The following is another example of a conventional gate driver circuit. The capacitor is charged during the semiconductor device remains off. When the semiconductor device is turned on, the input capacitance of the semiconductor device undergoes initial charge quickly by forward-direction high voltage as an in-series combined voltage of the power source voltage and the charged voltage of the capacitor, so that the semiconductor device turns on quickly (see Patent literature 2).